The present invention pertains to global positioning system (GPS) navigation and more particularly to odometer assisted GPS navigation.
The GPS system may be used for the location of vehicles. In such a system, the vehicle equipped with a GPS receiver and a processor receives signals from at least three of a constellation of GPS satellites and triangulates to self-determine its own position. Line of sight transmission from a satellite to a vehicle is extremely important since the vehicle must be able to receive the satellites' signals. If the vehicle is unable to accurately receive the satellite signals, proper position of the vehicle may not be able to be determined. A problem exists in a city's urban canyons, streets with high rise buildings surrounding it. The urban canyon provides for blocking the GPS satellite signals from being received by a vehicle. As a result, the vehicle's GPS receiver may be unable to receive at least three satellite signals to adequately self-determine its position. The vehicle's odometer can provide distance travelled information, but the heading of the vehicle needs to be determined to find the vehicle's position.
One solution to this problem is to use gyroscope technology to assist the GPS when GPS is not operational in urban canyons. Low cost gyroscope technology is not well developed at present.
A second solution may include the application of magnetic compasses when in an urban canyon. Magnetic compasses are unreliable in environments such as urban canyons in which there are many buildings made of steel which will affect the magnetic compass adversely.
Lastly, a differential odometry solution may be employed to solve the problem of GPS satellite signal loss in an urban canyon. This solution may be effective if it is already built in to the vehicle. If it is to be installed, the solution then becomes very expensive because sensors must be placed at the wheels of the vehicle in an accurate position. This is an expensive proposition to retrofit to vehicles. Also, the sensors are extremely sensitive to skidding of the vehicle with brakes locked.
Accordingly, what is needed is a low cost system to augment a basic GPS receiver for vehicle location in urban canyons.